To improve the cleanliness of various alloys, especially various alloys such as steel, which are cast by bottom pouring methods, it is particularly useful to filter the metal through a ceramic foam filter. The effect of this filter is to remove particulate inclusions and, in some cases, liquid inclusions. Thus, the filtration procedure has a beneficial effect on the quality of the resultant metal ingots. A variety of molten metal filters are known in the art, such as described in U.S. Pat. No. 3,962,081.
Bottom pouring casting methods generally involve the use of a common sprue and a plurality of ingot molds and runners from the common sprue to the ingot molds. The filter may be placed in a small tundish between the ladle and the top of the sprue. Alternatively, there are advantages in placing the filter directly upstream of the ingot butt.
However, each of these procedures suffers from disadvantages. Placing the filter at the top of the sprue permits reoxidation of the melt downstream of the filter. Also, a large amount of metal flow must be accommodated by a filter at the top of the sprue since all metal for the plurality of ingot molds passes through the sprue.
As indicated above, placing the filter directly in the ingot butt offers advantages. This installation is relatively simple, allows minimum opportunity for reoxidation of the melt downstream of the filter and enables the use of a plurality of filters to accommodate each ingot individually with a resultant smaller total metal throughput through the filter than would be provided with a common filter at the top of the sprue. However, this method also has certain shortcomings. It can be difficult to prime the filter with the molten metal. There is little opportunity for preheating the filter. Also, the filter is subject to high mechanical stresses resulting in the possibility of breakage. For example, sprues are commonly 10 to 20 feet high and therefore a large metallostatic head is built up.
It is an object of the present invention to provide an apparatus for casting molten metal using a metal filter and using the bottom pour method.
It is a further object of the present invention to provide an apparatus as aforesaid which utilizes the filter directly upstream of the ingot butt.
It is a still further object of the present invention to provide an apparatus as aforesaid which enables convenient priming of the filter and which minimizes mechanical stresses resulting in the possibility of breakage.
It is a further object of the present invention to provide an apparatus as aforesaid which is simple, convenient and expeditious to use on a commercial scale.
Further objects and advantages of the present invention will appear hereinbelow.